Toads inspire new muscle model

Published: Tuesday, June 3, 2008, 12:25 [IST]

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Washington, June 3 : Frogs and chameleons capture their prey by darting their long muscular tongue out and back inside their mouth in a flash. This mechanism has now given researchers a new insight into how muscles work and may help them in developing a new muscle model.

While it was long believed that muscles work like a motor, Northern Arizona University researcher Kiisa Nishikawa has now suggested that they actually act more like a spring.

Now, this new viewpoint may help the researchers in designing more efficient electric motors, better prostheses and new medical treatments for neuromuscular diseases like Parkinson's.

"Existing theories don't explain how muscles shorten rapidly. Muscles can only shorten to do work; they can't do work by lengthening," Nishikawa said.

Similarly, a spring can also only do work by shortening. For example, she said that the jaw muscles in toads and chameleons shorten in the lower jaw, and the opening of the jaws causes the tongue to stretch by its own momentum.

"When a toad or chameleon captures prey with its tongue, it exerts force over a distance. Figuring out how they do it has immense application to any device that actually moves," she added.

In fact, a toad's jaw muscles can produce forces much more than 700 times the animal's weight.

"The best electric motor achieves about one-third of that force-to-weight ratio," noted Nishikawa.

Besides, muscles also function as self-stabilizing springs.

"They have built-in self-correcting mechanisms. Before the brain can even react, muscles are changing their elasticity adaptively," said Nishikawa.

Think of walking down a flight of steps and missing a step. Leg muscles instantly become less stiff to afford better shock absorption. "It's an intrinsic property of muscle," she said.

And now Tom Sugar and his colleagues at Arizona State University have designed a robotic tendon.

Working at ASU's Human Machine Integration Laboratory, Sugar and his team are building "SPARKy" (Spring Ankle with Regenerative Kinetics) that mimics biology by storing and releasing energy during the ankle gait cycle.

"Energy is stored as the leg and body rolls over the ankle, and then this energy is released in a powerful burst to propel the user forward. By mimicking biology, we are able to build a very lightweight and functional device," said Sugar.

"Putting motors and springs together in a smart way is something nature hit on about 600 million years ago (with the earliest vertebrates)," said Nishikawa.

Nishikawa's studies of the neuromuscular basis for extremely rapid movements in animals, such as the toad snaring prey with its tongue, could leapfrog to a new model of muscle function, changing the standard representation of muscle as a motor.